1. Field of the Invention
The invention relates to a semiconductor laser driving system for driving a semiconductor laser element and more particularly to a semiconductor laser driving system which can change the intensity of the laser beam, at high speed, emitted from the semiconductor laser element.
2. Description of the Prior Art
In a conventional semiconductor laser driving system of this type, as is disclosed in Japanese examined patent publication No. 14585/89, a semiconductor laser element is turned on and off according to recording signals which are applied to the semiconductor laser driving system. When the recording signal indicates that a white color image is to be formed on a recording sheet, the semiconductor laser driving system applies an electric current, corresponding to the recording signal, to the semiconductor laser element so that the semiconductor laser element emits a laser beam, that strikes the photosensitive material, based on the electric current. When the recording signal indicates that a black color image is to be formed on a recording sheet, the semiconductor laser driving system does not apply an electric current to the semiconductor laser element and the semiconductor laser element does not emit a laser beam to strike the photosensitive material.
In the conventional semiconductor laser driving system, a constant electric current is applied to the semiconductor laser element when the semiconductor laser element is turned on based on the recording signal, so that the semiconductor laser element emits a constant level laser beam if the temperature of the semiconductor laser element is constant.
However the semiconductor laser element has the disadvantage that it spends a long period of time turning the laser element on and off. As the result, the recording apparatus employing the known semiconductor laser driving system has the disadvantage that the recording speed is low.